Directional microphone for hearing aid

ABSTRACT

The disclosure is directed to an improvement in a microphone used primarily in head-worn hearing aids in which the microphone achieves a directional characteristic. The chamber and aperture in front of the diaphragm or other speech-responsive member is constructed in the normal manner while the chamber to the rear of the diaphragm or other speech-responsive member has a plurality of hollow elongated members secured within the walls of the microphone housing. The elongated members may be formed from sintered porous material such as metal, glass, or plastic, and may be arranged side-by-side or in a honeycomb arrangement. The elongated members attenuate the propagation of the sound waves, the attenuation being approximately 20 decibels lower than that reaching the other side of the diaphragm or other speechresponsive member without materially changing the inherent response characteristic of the microphone.

United States Patent Hassler et a1.

[54] DIRECTIONAL MICROPHONE FOR HEARING AID [72] Inventors: OttoHassler; Johannes Wittkowski, both of Hamburg, Germany Willco-HorgerateMedizinische Appgratebau GmbH, Hamburg, Germany [22] Filed: Sept. 25,1970 [21] Appl. No.: 75,548

[73] Assignee:

Related U.S. Application Data [63] Continuation of Ser. No. 682,346,Nov. 13, 1967,

[451 May 9,1972

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas L. KundertAt!0rney1-i. Dale Palmatier [5 7] ABSTRACT The disclosure is directed toan improvement in a microphone used primarily in head-wom hearing aidsin which the microphone achieves a directional characteristic. Thechamber and aperture in front of the diaphragm or otherspeech-responsive member is constructed in the normal manner while thechamber to the rear of the diaphragm or other speech-responsive memberhas a plurality of hollow elongated members secured within the walls ofthe microphone housing. The elongated members may be formed fromsintered porous material such as metal, glass, or plastic, and may bearranged side-by-side or in a honeycomb arrangement. The elongatedmembers attenuate the propagation of the sound waves, the attenuationbeing approximately 20 decibels lower than that reaching the other sideof the diaphragm or other speech-responsive member without materiallychanging the inherent response characteristic of the microphone.

9 Claims, 2 Drawing Figures TRANSDUCER DIRECTIONAL MICROPHONE FORHEARING AID This application is a continuation of Ser. No. 682,346,filed Nov. 13, 1967, and now abandoned.

This invention relates to a microphone for hearing aids and, inparticular, to a small and miniature microphone for use on head-wornhearing aids, such as the spectacle type or the type worn behind theear.

Numerous attempts have been made in devising microphones for use withhearing aids in which a sense of direction is achieved which identifiesthe sound-emitting source. Generally such constructions are somewhatbulky and cumbersome, generally consisting of using two microphones in aback-to-back relationship. One such construction is that in a co-pendingapplication, filed Dec. 6, 1966, Ser. No. 599,505, now US. Pat. No.3,458,668 entitled Transducer For Head Worn Hearing Aid and assigned tothe same assignee. Another variation shown in the co-pending applicationmakes use of a pair of diaphragms for imparting movement to thesound-responsive member within the microphone.

In contrast thereto, the present invention makes use of a microphone inwhich a plurality of propagation-retarding acoustic resistances areformed in a chamber to the rear of the diaphragm of the microphone andin a general direction facing away from the direction of observation ofthe hearing aid wearer. The propagation-retarding acoustic resistancesare provided in elements forming a plurality of narrow passages withinthe chamber adjacent the diaphragm. A preferred form of the embodimentfor the propagation-retarding acoustic resistance elements is achievedby arranging a plurality of capillary tubes which are generallyassembled into a block, the block being situated in the chamber at therear of the diaphragm. Another embodiment of the invention is achievedby providing a plurality of fine hairs, such as that of a camel withinthe confines of the chamber to the rear of the diaphragm, the fine hairscreating the plurality of substantially narrow and parallel passages. Toachieve an optimum directional effect with the microphone, thedimensions of the propagation wave-retarding resistances are chosen sothat upon the pressure of the sound impinging upon the diaphragm fromthe referred direction reaching a maximum sound level, the soundpressure acting upon the rear of the diaphragm at the same time is at aminimum level, providing a ratio of the front pressure to the backpressure with a maximum value. It has been found that in forming thepropagation wave-retarding resistances, the best results are achieved bythe use ofa block" formed from a plurality of capillary tubes in whichthe ratio of their length to their cross section is made very large andthe overall or passage cross section of the tubes correspondapproximately to the effective area of the diaphragm. While thiscondition may be somewhat difficult to achieve without enlarging thecross section of the microphone by the use of capillary tubes,considering even a minimum wall thickness, it has been found that glass,metal, or certain synthetic plastics are quite acceptable and whensintered form a block of the appropriate dimensions as just mentioned.It has been found that a honeycomb-type arrangement of the capillarytubes produces a very favorable ratio of the free soundadmitting crosssection to the total cross section. It has also been found that thecertain corrugated foils of metal or synthetic plastic materials may berolled or folded to form a pack or block of capillary tubes such as justdescribed. It will also be found that the invention can be used withelectro-magnetic type transducers or a piezo-electric transducer used asthe element for changing the sound to an electrical signal within themicrophone.

It is, therefore, a general object of this invention to provide ahearing aid microphone for use on the head having a constructionenabling the wearer to recognize the direction from which sound isemitting.

It is still another object of this invention to provide a microphone inwhich a propagation-retarding acoustic resistance mechanism isconstructed in the portion oriented away from the direction from whichit is desirable to detect the sound.

It is another object of this invention to provide in a microphone foruse with a head-worn hearing aid, an acoustic resistance mechanismhaving a cross-sectional area which corresponds to the effective area ofthe sound pressure responsive member.

It is another object of this invention to provide a directionalmicrophone for use with a head-worn hearing aid in which the soundreaching a responsive member facing away from the desired direction isapproximately 20 decibels lower than the sound reaching the other sideof the sound-responsive member.

These and other objects and advantages of the invention will more fullyappear from the following description, made in connection with theaccompanying drawings, wherein like reference characters refer to thesame or similar parts throughout the several views, and in which:

FIG. 1 is a diagrammatic longitudinal section of a typical microphone;and

FIG. 2 is a diagrammatic illustration of a frequencyresponse curveshowing the operational effect of the microphone.

As found in FIG. 1, a microphone housing 11, has enclosed therein, atransducer or converter system 12, which as mentioned previously, may beof the electro-magnetic or piezoelectric type. Transducer 12 isconnected through a coupling pin 13 to a diaphragm 14, which is securedin the normal manner to the outer edges of housing 11. Diaphragm 14 issecured at a spacially disposed position from the end wall of housing 11so that a chamber 15 is formed therein and an aperture 16 is formed inthe end of the housing to admit the sound waves to impinge upondiaphragm 13.

Another chamber 17 is formed to the rear of diaphragm 14 by the use of ablock of propagation-retarding acoustic resistance material 18 which maybe in one of the forms previously described. The entire rearwardlyfacing end of housing 11 is open to create another aperture 19. Thussound waves entering through aperture 19 pass through the block ofpropagation-retarding acoustic resistance material in order to reachchamber 17 and thus provide an actuating motion to diaphragm 14.

FIG. 2 shows a frequency-response curve for sound waves detected by themicrophone emanating from a preferred direction for detection by themicrophone. Curve 20 is a frequency-response curve for a microphone ofnormal construction receiving the sound propagated waves from thepreferred direction. Curve 21 corresponds to the frequency response ofthe present invention for sound received from the preferred directionthrough aperture 16. Curve 22 is the frequency-response curve for soundpropagated waves arriving at the aperture 19 of the structure as seen inFlG. 1 when directed from a direction opposite to the preferreddirection. It will be observed that the decibel difference betweencurves 21 and 22 exhibits the ratio of the gain of the microphonebetween the two directions of sound reception. lt will be seen that amean value of approximately 20 decibels is achieved throughout thepredominance of the audio range which insures that the user of such amicrophone will be assured of directional hearing.

It will be observed that the effective area of diaphragm 14 isapproximated by the cross-sectional area of housing 11 and aperture 19,the compartment being enclosed with the block of extremely finecapillary tubes or other appropriate material as set forth herein. Itwill also be observed that the microphone has achieved a directionalcharacteristic which is somewhat kidney shaped when worn upon the headas opposed to the general microphone pickup characteristics which aregenerally spherical in nature.

It will, of course, be understood that various changes may be made inthe form, details, arrangement, and proportions of the parts withoutdeparting from the scope of the invention which consists of the mattershown and described herein and set forth in the appended claims.

What is claimed is:

1. An improved miniature microphone constructed and arranged to be usedin a hearing aid housing to be worn on the head of the wearer whereinthe improvement comprises:

a miniature elongated microphone housing having a substantially enclosedend and an open end, said enclosed end having a sound admitting apertureformed therein which is considerably smaller than said open end,

a sound pressure-responsive member secured to said hous ing and disposedbetween said ends to define first and second chambers therebetween, saidpressure-responsive member adapted to be coupled to a transducer formovement by sound waves;

a transducer for producing electrical signals representative of soundwaves operably connected to said sound pressure-responsive member andsecured within said second chamber in said housing; and

a propagation-retarding acoustic resistance mechanism disposed withinand obstructing said open end of the housing, said mechanism forming aplurality of narrow elongated passages, each having substantially thesame length to admit the sound waves to said sound pressureresponsivemember, said mechanism containing a plurality of elongated elements injuxtaposition arrangement forming said plurality of narrow elongatedpassages and extending between the open end of said housing and saidtransducer in said second chamber, said transducer producing electricalsignals from sound waves received through said acoustic resistancemechanism which has a frequency response having a profile substantiallythe same as that produced by said transducer from sound waves receivedfrom said aperture.

2. The invention set forth in claim 1 wherein said open end of thehousing having said propagation-retarding acoustic resistance mechanismdisposed therein has a cross-sectional area substantially equal to theeffective area of said sound pressure-responsive member.

3. The invention set forth in claim 1 wherein said propagation-retardingacoustic resistance mechanism produces an acoustic attenuation having ameans value of substantially decibels higher than that for sound wavesentering the aperture of the substantially enclosed end of the housing.

4. A microphone for a hearing aid to be worn on a persons head fordetecting a sound and discriminating the direction of the source of thesound, comprising a sound pressure-responsive diaphragm having oppositesides,

an electric signal-generating transducer connected to the diaphragm andproducing such signals in response to diaphragm movement,

a housing confining and mounting the diaphragm and defining open andsubstantially enclosed chambers respectively disposed at the oppositesides of the diaphragm, the housing having a sound admitting aperturecommunicating with the substantially enclosed chamber, the open chamberbeing disposed to the rear of the diaphragm and having an open end toface away from the source of sound, the housing defining unobstructedspace adjacent the transducer to freely transmit sound past thetransducer and to the diaphragm,

and a sound wave propagation-retarding acoustic resistance mechanismobstructing the open rear end of the open chamber, said mechanismincluding a plurality of elongate and substantially parallelcapillaries, the individual capillaries having a size of opening of theorder of the size of passages existing between confined camel hairs, andsaid capillaries being assembled into a block and confined in theelongate open chamber of the housing the open ends of the capillariesconfronting the open end of the open chamber to face the directionopposite the source of sound, the sound waves creating minimum andmaximum pressures impinging the diaphragm and producing movementthereof, the sound wave propagation being retarded by the resistancemechanism to the extend that at the time the sound waves impinge thefront side of the diaphragm with a maximum pressure, the sound wavesimpinge the back side of the diaphragm with less than maximum pressure,whereby to achieve directional effect with the microphone.

5. The invention according to claim 4 and the overall open cross sectionof the capillaries corresponding approximately to the effective area ofthe diaphragm.

6. The invention according to claim 4 and the overall open cross sectionof the capillaries being approximately the same as the effective area ofthe open end of the open chamber.

7. The invention according to claim 4 and the dimensions of thepropagation wave-retarding resistance mechanism includ ing thecapillaries being dimensioned to maximize the ration of the sound wavepressures applied against the front of the diaphragm in relation to suchpressures applied to the back of the diaphragm.

8. A microphone for a hearing aid to be worn on a person's head fordetecting a sound and discriminating the direction of the sound,comprising,

a sound pressure-responsive diaphragm having front and back sides,

an electric signal-generating transducer connected to the diaphragm andproducing such signals in response to diaphragm movement,

a housing confining and mounting the diaphragm and defining open andsubstantially enclosed chambers respectively disposed at the back andfront sides of the diaphragm, the housing having a sound-admittingaperture communicating with the substantially enclosed chamber, the openchamber being elongate and disposed at the rear of the housing andhaving an open rear end to face away from the source of the sound andfor admitting sound for propagation to the back side of the diaphragm,

a sound wave propagation-retarding acoustic resistance mechanismobstructing the open rear end of the open chamber, said mechanismincluding a plurality of elongate and substantially parallelcapillaries, the individual capillaries having a size of opening of theorder of the size of the discrete passages existing between confinedcamel hairs, said capillaries being assembled into a block and confinedin the elongate open chamber of the housing, the capillaries in theblock extending generally longitudinally of the chamber and toward theopen end thereof, the open ends of the capillaries confronting the openend of the chamber to face the direction opposite the source of sound,the sound waves creating maximum and minimum pressures impinging thediaphragm and producing movement thereof, the sound wave propagationbeing retarded by the resistance mechanism to the extent that at thetime the sound waves impinge the front side of the diaphragm with amaximum pressure, the sound waves impinge the back side of the diaphragmwith substantially minimum pressure, to thereby substantially maximizethe ratio of sound wave pressure applied against the front and backsides of the diaphragm, whereby to achieve a significant directionaleffect with the microphone.

9. A directional microphone for use in a hearing aid to be worn on apersons head, comprising;

a diaphragm sensitive to sound pressure;

a diaphragm-operated transducer generating electric signals related tothe sound pressures sensed by the diaphragm;

a microphone housing enclosing the diaphragm and defining front and rearchambers at opposite sides of the diaphragm, the housing having a soundopening communicating with the front chamber and freely admitting soundpressures to impinge upon the diaphragm; and

means defining clear passages into the rear chamber of the housing at alocation remote from the sound opening said passages having a sizeadmissive to sound pressures and also resistive to transmission of suchsound pressures to retard impingement of the sound pressures against thediaphragm, the retardation effected by the clear passages causing soundpressure from the preferred direction acting upon the rear of thediaphragm being at a minimum level while sound pressure admitted throughthe sound opening at the rear of the diaphragm reaches a maximum level.5

I UNITED STATES PATENT OFFICE v I QERTEFECATE @F (IQRRECTIQN Patent No.3 662 124 Dated Max 9 1972 Inventor) Otto Hassler; Johannes WittkowskiIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

[73] Assignee: Change "Appgratebau" to -Apparatebau.

In claim 3 column 3 line 40, please change "means" to mean.

Signed and sealed this 12th day of September 1972.

( EA Attest:

EDWARD M.FLETCHER,JR. ROBERT GOT'ISCHALK Attesting Officer Commissionerof Patents 2- uscoMM-oc 60376-P69 0.5. GOVERNMENT PRiNTlNG OFFICE: I9690-365-314

1. An improved miniature microphone constructed and arranged to be usedin a hearing aid housing to be worn on the head of the wearer whereinthe improvement comprises: a miniature elongated microphone housinghaving a substantially enclosed end and an open end, said enclosed endhaving a sound admitting aperture formed therein which is considerablysmaller than said open end, a sound pressure-responsive member securedto said housing and disposed between said ends to define first andsecond chambers therebetween, said pressure-responsive member adapted tobe coupled to a transducer for movement by sound waves; a transducer forproducing electrical signals representative of sound waves operablyconnected to said sound pressureresponsive member and secured withinsaid second chamber in said housing; and a propagation-retardingacoustic resistance mechanism disposed within and obstructing said openend of the housing, said mechanism forming a plurality of narrowelongated passages, each having substantially the same length to admitthe sound waves to said sound pressure-responsive member, said mechanismcontaining a plurality of elongated elements in juxtapositionarrangement forming said plurality of narrow elongated passages andextending between the open end of said housing and said transducer insaid second chamber, said transducer producing electrical signals fromsound waves received through said acoustic resistance mechanism whichhas a frequency response having a profile substantially the same as thatproduced by said transducer from sound waves received from saidaperture.
 2. The invention set forth in claim 1 wherein said open end ofthe housing having said propagation-retarding acoustic resistancemechanism disposed therein has a cross-sectional area substantiallyequal to the effective area of said sound pressure-responsive member. 3.The invention set forth in claim 1 wherein said propagation-retardingacoustic resistance mechanism produces an acoustic attenuation having ameans value of substantially 20 decibels higher than that for soundwaves entering the aperture of the substantially enclosed end of thehousing.
 4. A microphone for a hearing aid to be worn on a person''shead for detecting A sound and discriminating the direction of thesource of the sound, comprising a sound pressure-responsive diaphragmhaving opposite sides, an electric signal-generating transducerconnected to the diaphragm and producing such signals in response todiaphragm movement, a housing confining and mounting the diaphragm anddefining open and substantially enclosed chambers respectively disposedat the opposite sides of the diaphragm, the housing having a soundadmitting aperture communicating with the substantially enclosedchamber, the open chamber being disposed to the rear of the diaphragmand having an open end to face away from the source of sound, thehousing defining unobstructed space adjacent the transducer to freelytransmit sound past the transducer and to the diaphragm, and a soundwave propagation-retarding acoustic resistance mechanism obstructing theopen rear end of the open chamber, said mechanism including a pluralityof elongate and substantially parallel capillaries, the individualcapillaries having a size of opening of the order of the size ofpassages existing between confined camel hairs, and said capillariesbeing assembled into a block and confined in the elongate open chamberof the housing the open ends of the capillaries confronting the open endof the open chamber to face the direction opposite the source of sound,the sound waves creating minimum and maximum pressures impinging thediaphragm and producing movement thereof, the sound wave propagationbeing retarded by the resistance mechanism to the extend that at thetime the sound waves impinge the front side of the diaphragm with amaximum pressure, the sound waves impinge the back side of the diaphragmwith less than maximum pressure, whereby to achieve directional effectwith the microphone.
 5. The invention according to claim 4 and theoverall open cross section of the capillaries correspondingapproximately to the effective area of the diaphragm.
 6. The inventionaccording to claim 4 and the overall open cross section of thecapillaries being approximately the same as the effective area of theopen end of the open chamber.
 7. The invention according to claim 4 andthe dimensions of the propagation wave-retarding resistance mechanismincluding the capillaries being dimensioned to maximize the ration ofthe sound wave pressures applied against the front of the diaphragm inrelation to such pressures applied to the back of the diaphragm.
 8. Amicrophone for a hearing aid to be worn on a person''s head fordetecting a sound and discriminating the direction of the sound,comprising, a sound pressure-responsive diaphragm having front and backsides, an electric signal-generating transducer connected to thediaphragm and producing such signals in response to diaphragm movement,a housing confining and mounting the diaphragm and defining open andsubstantially enclosed chambers respectively disposed at the back andfront sides of the diaphragm, the housing having a sound-admittingaperture communicating with the substantially enclosed chamber, the openchamber being elongate and disposed at the rear of the housing andhaving an open rear end to face away from the source of the sound andfor admitting sound for propagation to the back side of the diaphragm, asound wave propagation-retarding acoustic resistance mechanismobstructing the open rear end of the open chamber, said mechanismincluding a plurality of elongate and substantially parallelcapillaries, the individual capillaries having a size of opening of theorder of the size of the discrete passages existing between confinedcamel hairs, said capillaries being assembled into a block and confinedin the elongate open chamber of the housing, the capillaries in theblock extending generally longitudinally of the chamber and toward theopen end thereof, the open ends of the capillaries confronting the openend of the chamber to face the direction opposite the source of sound,the sound waves cReating maximum and minimum pressures impinging thediaphragm and producing movement thereof, the sound wave propagationbeing retarded by the resistance mechanism to the extent that at thetime the sound waves impinge the front side of the diaphragm with amaximum pressure, the sound waves impinge the back side of the diaphragmwith substantially minimum pressure, to thereby substantially maximizethe ratio of sound wave pressure applied against the front and backsides of the diaphragm, whereby to achieve a significant directionaleffect with the microphone.
 9. A directional microphone for use in ahearing aid to be worn on a person''s head, comprising: a diaphragmsensitive to sound pressure; a diaphragm-operated transducer generatingelectric signals related to the sound pressures sensed by the diaphragm;a microphone housing enclosing the diaphragm and defining front and rearchambers at opposite sides of the diaphragm, the housing having a soundopening communicating with the front chamber and freely admitting soundpressures to impinge upon the diaphragm; and means defining clearpassages into the rear chamber of the housing at a location remote fromthe sound opening said passages having a size admissive to soundpressures and also resistive to transmission of such sound pressures toretard impingement of the sound pressures against the diaphragm, theretardation effected by the clear passages causing sound pressure fromthe preferred direction acting upon the rear of the diaphragm being at aminimum level while sound pressure admitted through the sound opening atthe rear of the diaphragm reaches a maximum level.